Human Genetics: Patterns of Inheritance for Human Traits

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Human GeneticsPatterns of Inheritance for
Human Traits
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We will be discussing 5 Patterns of Inheritance
for Human Traits

• 1. Single Allele Dominant
• 2. Single Allele Recessive
• 3. Sex Linked (X-Linked)
• 4. Multiple Alleles
• 5. Polygenic Traits

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Single Allele Genes

• Regular traits that are either determined by a
  dominant or recessive allele on an autosome
• Autosomal Dominant examples
• a. Huntingtons Disease
• b. Achondroplasia (dwarfisim)
• c. Polydactyly (extra fingers and toes)
• 2. Autosomal Recessive examples
• a. Albinism
• b. Cystic Fibrosis
• c. Sickle Cell Anemia

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1. Dominant Allele Disorders

• Huntingtons Disease (HD)
• Results in loss of muscle control and mental
  deterioration
• No signs are shown until 30s
• Brain degeneration
• Treatment No cure, but drug treatments are
  available to help manage symptoms.

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1. Dominant Allele Disorders

• Achondroplasia
• Dwarfism
• Person grows no taller than 44

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1. Dominant Allele Disorders

• Polydactyly
• The presence of more than the normal number of
  fingers or toes.
• Can usually be corrected by surgery.

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2. Recessive Allele Disorders

• Albinism
• Lack of pigment in skin, hair, and eyes
• Mutation in one of several genes which provide
  the instructions for producing one of several
  proteins in charge of making melanin.

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2. Recessive Allele Disorders

• Cystic Fibrosis (CF)
• Caused by recessive allele on chromosome 7
• Small genetic change (removes one Amino Acid) ?
  changes protein
• Results in Excess mucus in the lungs, liver and
  digestive tract, gets infection easily, and early
  death unless treated.

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2. Recessive Allele Disorders

• Sickle Cell Disease
• Red blood cells are bent and twisted
• Get stuck in capillaries ? damage tissues
• Results in weakness, damage to brain and heart

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3. Sex Link TraitsGenes on the X and Y
chromosomes
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Human Chromosomes 2 Sex Chromosomes
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Human Chromosomes44 Autosomes
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Gender

• We determine the gender of an individual through
  sex chromosomes
• Sex Chromosomes X and Y
• Female XX
• Male XY
• The father gives an X or Y to the gametes. The
  mother only gives an X to the gamete
• The X chromosome is larger than the Y chromosome.

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What are sex-linked genes? ? genes found on a
sex chromosome

• X-linked genes are genes found on the X
  chromosome, symbolized by Xr, XR, Y0.
• Y-linked genes are found on the Y chromosome,
  symbolized by X0, YR, Yr

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Sex-Linked Traits

• It is possible for a female to be a carrier of an
  X-linked trait, but not express it
• Men will express all X-linked traits they inherit
  because they have one X chromosome

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X-linked Genes

• Lets do a punnett square for a female carrier of
  an x-linked gene and a recessive male
• What will the genotypes be?
• XRXr and XRY

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Heres the results

• For girls 0 have the trait
• For boys 50 have it.
• Probability is higher for boys because whatever X
  they get determines the trait, for girls they
  have to get 2 recessive Xs.

XR Xr
XR XR XR XR Xr
Y0 XR Y0 Xr Y0
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Examples of X-linked traits

• 1. Color Blindness
• 2. Hemophilia
• 3. Muscular Dystrophy
• 4. Icthyosis simplex (scaly skin)

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Colorblindness

• A person with normal color vision sees a number
  seven in the circle above.
• Those who are color blind usually do not see any
  number at all.

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Colorblindness

• RED-GREEN COLORBLINDNESS
• People with red-green color blindness see either
  a three or nothing at all.
• Those with normal color vision see an 8.

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Hemophilia

• Hemophilia- Lacking in the ability to clot blood
• There is a gene on the X chromosome that
  control blood clotting
• People who have hemophilia are missing the
  protein to clot blood
• They can bleed to death by minor cut.

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Muscular Dystrophy

• - Results in weakening/loss of muscles
• - Caused by defective version of gene that codes
  for muscle

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Sex-influenced Traits

• Sex-Influenced traits are those that are on
  autosomes, but occur because of the sex hormones
  in male and female bodies.
• Examples Facial hair
• Baldness

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4. Multiple Alleles

• Multiple Alleles any gene that has 3 or more
  alleles (not just 1 dominant and 1 recessive)
• Example Blood type has 3 alleles
• IA Type A blood (dominant)
• IB Type B blood (dominant)
• i Type O blood (recessive)

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Check out the possible genotypes and phenotypes
of blood below
Genotypes Phenotypes
IAIA or IAi Type A
IBIB or IBi Type B
IAIB Type AB
ii Type O
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Blood has both Multiple Alleles and is CoDominant

• If you have IAIB as your genotype, you have both
  Type A and Type B blood,
  also known as Type AB
• If you have IAi, i is recessive
  to IA, so you have type A blood
• Q. When would you have Type O blood?
• A. When you have ii as your genotype.

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5. Polygenic Traits traits controlled by 2 or
more genes that interact, forming the trait

• Usually show a wide range of phenotypes
• Ex Skin color, eye color, foot size, height
• Wide range of skin colors because there are more
  than 4 genes that control this trait.
• These may also be influenced by the environment,
  for example height. If not given the proper
  nutrition as a child, they might not be as tall
  as their genes dictate.